1. Field of the Invention
This invention relates to a process for developing a silver halide photographic emulsion, which provides an ultra high contrast negative image, excellent dot quality and excellent tonal gradiation.
2. Description of the Prior Art
A method of obtaining photographic characteristics of a high contrast negative image by adding a hydrazine compound to a silver halide photographic emulsion is described in U.S. Pat. No. 2,419,975. U.S. Pat. No. 2,419,975 discloses that extremely high contrast photographic characteristics, such as a gamma (.gamma.) of more than 10, can be obtained by adding a hydrazine compound to a silver chlorobromide emulsion and developing the emulsion with a developer having a pH as high as 12.8. However, strongly alkaline developers having a pH near 13 are so unstable that they tend to be oxidized by air and, therefore, cannot be used or stored for long periods of time. Moreover, development at such a high pH tends to cause fog.
However, it is known that the high contrast photographic characteristics of a gamma of as high as more than 10 as described in U.S. Pat. No. 2,419,975 are still insufficient to obtain satisfactory dot quality and tonal gradation for platemaking using, for example, a contact screen, and that infectious development characteristics as are obtained by using a lithographc developer containing a sulfite at a low concentration are necessary for attaining these objects.
U.S. Pat. No. 3,386,831 describes a process for stabilizing an emulsion by adding a mono-phenylhydrazide of an aliphatic carboxylic acid to an essentially surface-sensitive photographic silver halide emulsion. The object and effect of U.S. Pat. No. 3,386,831 is different from the objects and effect of the present invention.
On the other hand, Japanese Patent Application (OPI) No. 19836/72 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application") corresponding to U.S. Pat. No. 3,972,719 describes a process for obtaining photographic characteristics suitable for the reproduction of dot images or lines using a stable developer. Japanese Patent Application (OPI) 19836/72 contains the description that images with good dot quality can be obtained by developing a silver halide light-sensitive material with a developer containing (1) a p-dihydroxybenzene derivative, (2) at least 5 g/l sulfite ion and (3) a nitroindazole or nitrobenzimidazole compound. However, this process is still unsatisfactory from a practical standpoint for producing a photographic plate for plate-making containing dot images, since the developer results in inferior dot quality as compared with a conventional lithographic type developer although stability of the developer is improved to some extent. In addition, this process has the defect that the dot quality seriously deteriorates as the sulfite ion concentration is increased for stabilizing the developer.
Also, it is known that high contrast silver halide light-sensitive materials are generally so sensitive to the products formed by development that localized developing effects occur. In particular, when such light-sensitive materials are developed using an automatic developing machine, the phenomenon that the density at the area adjacent the area where development occurs only slightly becomes high due to excess development whereas the density at the area adjacent the area where development sufficiently occurs becomes low due to inhibition of development. This phenomenon is called "drag streaks" and, particularly in the case of conducting development using an automatic developing machine, drag streaks tend to occur since films are conveyed in a definite direction.
As is described above, obtaining excellent dot quality and tonal gradation with ultra high contrast photographic characteristics which is useful in the reproduction of lines has been eagerly desired using a stable developer. In addition, development of a process for reducing drag streaks has been strongly desired.